Conventional handsets in Global System for Mobile telephony (GSM) devices today have normally only one receiver/transmitter (RX/TX) that are used for connecting to a GSM radio system over a radio interface. Hence, the handset can only transmit and receive on one frequency at the time.
The base stations used for establishing the radio interface to the GSM system similarly have a limited number of transmitters/receivers. There is a constant drive to minimize the number of transmitters/receivers in the base station to reduce costs both in terms of hardware but also in terms of maintenance. Thus, the number of transmitters/receivers should therefore be as low as possible without making the number so low that the quality of service to the subscribers is reduced to an unacceptable level. Also, the complexity of the transmitters/receivers should be low for reducing costs. In a typical base station there can be, for example, four transmitters/receivers for each cell served by the base station. In such a scenario, only one of the transmitters/receivers may be designed to support EGPRS because such a transceiver is more complex and hence more costly both to manufacture and to maintain.
In release 7 of the 3GPP specifications a downlink dual carrier is introduced. The downlink dual carrier GSM EDGE Radio Access Network (GERAN) makes it possible for the mobile station to receive data on two different frequencies simultaneously. The reason for adding a new downlink carrier is to increase the throughput for Enhanced GPRS (EGPRS). The second carrier enables the mobile station to receive twice as many time slots as with a conventional Enhanced GPRS (EGPRS) system. To be able to benefit from this new feature the mobile station needs to have two receivers. In addition each cell must have two transmitters supporting EGPRS. This is also described in the US patent application Nos. US20060092877 and US20060232741.
To provide each cell with two transmitters and in particular two transmitters having EGPRS may turn out to be unwarranted for a particular cell for the normal load. On the other hand subscribers may demand high throughput in all areas of the GSM network.
Hence, there exists a need for a method and a system that is able to provide high throughput and at the same time keep the costs for additional hardware in terms of transmitters, in particular complex base station transmitters, to a minimum.